Android Java Activity Lifecycle & Intent Navigation

A foundational Android development starter in Java demonstrating core Activity lifecycle management, Explicit Intent navigation, bundle payload transfer with putExtra, and user event handling.

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📖 Overview

The Java-Classes project demonstrates the foundational building blocks of native Android development using Java. Designed as a clean reference for Android application architecture, it illustrates how Android activities operate, how inter-component communication is achieved via the Android Intent messaging framework, and how data is transferred across screens safely.

🎯 Key Learning Objectives

• Activity Lifecycle & Declarative Layout Binding: Understanding onCreate(Bundle savedInstanceState) and setContentView().
• Explicit Intent Routing: Transitioning between distinct application activities using explicit class references (new Intent(MainActivity.this, SecondActivity.class)).
• Cross-Activity Data Passing: Packing primitive and string payloads into Intent Extras (intent.putExtra(key, value)) and extracting them in receiver activities (getIntent().getStringExtra(key)).
• User Input Validation & Event Handling: Handling button click events with Java 8 lambdas (v -> { ... }), managing input state, and presenting Android Toast notifications.
• Modern SDK Compatibility: Configured for Android 15 / SDK 36 using AndroidX AppCompat and ConstraintLayout.

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🏗️ Architecture & Component Flow

sequenceDiagram
autonumber
actor User as App User
participant Main as MainActivity
participant Intent as Explicit Intent (putExtra)
participant Second as SecondActivity
User->>Main: Enter name into EditText
User->>Main: Click "Greet" Button
Main->>Main: Validate input (!name.isEmpty())
alt Input is Valid
Main->>Intent: Instantiate Intent(MainActivity.this, SecondActivity.class)
Main->>Intent: putExtra("user_name", name)
Main->>Second: startActivity(intent)
Second->>Second: onCreate() -> getIntent().getStringExtra("user_name")
Second->>Second: Set TextView text to "Welcome [name]!"
Second-->>User: Display personalized greeting screen
else Input is Empty
Main->>User: Display Toast error ("Please enter your name")
end

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✨ Core Concepts & Code Walkthrough

1. Explicit Intent Creation with Extras Payload

In MainActivity.java, user input is verified and packaged into an explicit intent before launching the destination activity:

publicclassMainActivityextendsAppCompatActivity {
@OverrideprotectedvoidonCreate(BundlesavedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
EditTexteditTextName = findViewById(R.id.etName);
ButtonbuttonGreet = findViewById(R.id.buttonGreet);
TextViewtextViewGreets = findViewById(R.id.tvGreets);
buttonGreet.setOnClickListener(v -> {
Stringname = editTextName.getText().toString().trim();
if (!name.isEmpty()) {
textViewGreets.setText("Hello " + name + "!");
Intentintent = newIntent(MainActivity.this, SecondActivity.class);
intent.putExtra("user_name", name);
startActivity(intent);
} else {
textViewGreets.setText("Please enter your name");
Toast.makeText(this, "Please enter your name", Toast.LENGTH_SHORT).show();
}
});
}
}

2. Intent Payload Extraction

In SecondActivity.java, the receiving activity extracts the data payload from the launching intent during its onCreate lifecycle hook:

publicclassSecondActivityextendsAppCompatActivity {
@OverrideprotectedvoidonCreate(BundlesavedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
TextViewtextViewRecieved = findViewById(R.id.tvRecieved);
StringnameReceived = getIntent().getStringExtra("user_name");
textViewRecieved.setText("Welcome " + nameReceived + "!");
}
}

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📱 Project Structure

Java-Classes/
├── app/
│ ├── src/main/java/com/example/javaclasses/
│ │ ├── MainActivity.java # Primary launcher Activity with input validation
│ │ └── SecondActivity.java # Receiver Activity displaying unpacked data
│ ├── src/main/res/
│ │ ├── layout/
│ │ │ ├── activity_main.xml # Input form with ConstraintLayout
│ │ │ └── activity_second.xml # Display layout with TextView
│ │ └── values/ # Colors, styles, and strings
│ ├── src/main/AndroidManifest.xml # Activity declarations & intent filters
│ └── build.gradle.kts # Java 11 compilation, SDK 36 configuration
└── gradle/
└── libs.versions.toml # Version catalog

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🛠️ Technology Stack Matrix

Component	Technology	Version / Details
Platform	Android	API 24+ (Compile & Target SDK 36)
Language	Java	Java 11 (JavaVersion.VERSION_11)
Components	Android Activities & Intents	android.content.Intent, AppCompatActivity
UI Layout	Android ConstraintLayout	androidx.constraintlayout:constraintlayout
Design	Material Design Components	com.google.android.material:material
Build System	Gradle (Kotlin DSL)	AGP 8.8+

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🚀 Getting Started

Prerequisites

• Android Studio Ladybug (2024.2.1+) or newer.
• JDK 11 or JDK 17.
• Android SDK 36.

Build & Run

1. Clone the repository:

   git clone https://github.com/shayann07/Java-Classes.git
   cd Java-Classes

2. Open in Android Studio: Open the folder and allow Gradle sync to complete.
3. Assemble Debug Build:

   ./gradlew assembleDebug

4. Run on Device: Launch via Android Studio or command line onto an active emulator or physical test device.

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📄 License

This project is licensed under the MIT License — Copyright (c) 2026 shayann07.